The invention is directed to improvements in a fuel injection pump for internal combustion engines.
In such fuel injection pumps, the quantity of fuel delivered per pump piston stroke to the injection nozzles and injected there into the cylinders of the engine is metered highly accurately by the electric control mechanism. However, it has been found that the metered fuel quantity depends decisively on the temperature of the fuel being pumped, and thus can fluctuate within relatively wide limits, so that an optimally metered fuel injection quantity is not reliably assured.
However, the temperature dependency of the fuel injection can easily be compensated for by measuring the instantaneous temperature of the fuel pumped by the pump piston from the pump interior and then including this measured value in the computation of the control variable supplied to the electric control mechanism to serve as a correction variable for actuation of the quantity adjusting device.
In a known fuel injection pump (German Offenlegungsschrift 29 29 176), the entire overflow quantity of approximately 30 liters per hour flows out of the pump interior via a fluid-carrying opening into the control mechanism chamber, from whence it flows via the overflow valve into the fuel return system and thus returns to the fuel tank, which is at atmospheric pressure. The pump interior and control mechanism chamber are subjected to a continuous flow through them, and so the fuel temperature in the two chambers is approximately the same. Since the fuel, especially Diesel fuel, usually contains relatively large proportions of water, water can get into the electrical parts of the control mechanism that carry voltage, and if the water remains there for very long it can corrode and destroy those parts.
To avoid this corrosion problem, the fluid-carrying opening in the fuel injection pump of the usual type initially referred to above is embodied as a throttle, having an opening cross section of only a few square micrometers. Thus only a very small fuel quantity, of about 30 cm.sup.3 per hour, reaches the control mechanism chamber, and its water concentration is only 10% that of the fuel located in the pump interior. Since the low fuel inflow quantity causes virtually no turbulence in the fuel in the control mechanism chamber, the water settles to the bottom of the control mechanism chamber, where it cannot come into contact with currentcarrying parts of the electric control mechanism. In this fuel injection pump, no notable fuel flow takes place, even though the control mechanism is filled with fuel, and so the temperature of the fuel located in the control mechanism chamber is not a direct measure for the temperature of the fuel actually pumped out of the pump interior by the pump piston.